This invention relates to an air laydown process for assembling textile fibers into webs and is more particularly concerned with improvements in collecting textile fibers to form webs which are suitable for use in producing high quality nonwoven fabric.
Zafiroglu U.S. Pat. No. 3,797,074 discloses a process and apparatus for high speed production of uniform webs from feed batts of staple fibers. The batt is fed into a curved space between a toothed disperser roll, rotating at a surface speed of at least 3,000 feet per minute, and a stationary, smooth-surfaced curved disperser plate which is closely-spaced from the disperser roll teeth to hold the fibers close to the roll until a fiber-doffing position is reached at the tip of the disperser plate. At this location the fibers are projected, by tangential ejection from the roll, through an opening into duct means. Air supply directs a stable stream of air, of uniform velocity, low turbulence and low vorticity, through the duct in the direction of movement of the roll surface so that the fibers are projected into the stream as a thin or distinct fiber stream at an angle of less than about 25.degree. and preferably less than 12.degree. to the direction of air flow through the duct. The fibers are carried in the air stream to condenser means which separates the fibers from the air to form webs weighing from about 0.1 to 10 ounces per square yard as determined by the relative speeds of the fiber feed and condenser means.
The patent also discloses the use of a mixing stream generator to create a small amount of turbulence in the air stream which causes lateral mixing of fibers within the distinct layer being conveyed to the conveyor means (without dispersing the layer into a cloud of fibers) which reduces machine-direction streaks in the resultant condensed web. Unfortunately, this has not been satisfactory, especially at high speeds, in yielding uniform webs in other respects such as clumps (blotches) of fibers and cross-direction streaks. The mixing stream generator while reducing machine-direction streaks, increases blotchiness and has little effect on cross-direction streaks.
The process of the above patent provides webs which are of high quality relative to webs produced by previous processes. However, the webs are still subject to basis-weight variations which show up in the nonwoven fabrics prepared from the webs.